1. Field of the Invention
The invention relates to a one-piece contact spring comprising a box-shaped contact part having a top wall, side walls and a bottom wall, from which at least one spring arm is bent back into the interior of the contact part at the insertion opening, which, together with at least one additional spring arm forms a plug-in contact socket.
2. Brief Description of the Prior Art
Contact springs are generally known. They are employed preferably as connectors in automotive engineering in order to establish releasable contact points paying attention to increased contact safety.
Known contact springs usually are of multi-part design in order to thus ensure the afore-mentioned contact safety, especially by combination of different materials. In this regard, there is often provided a box-shaped contact part having resilient contact lugs in its interior which cooperate with the respective counter- or complementary contact.
However, it is also known,that different materials cause increased expenditure as regards the storage thereof. A plurality of separate parts to be joined together for constituting the finished product thus also means an increased assembly expenditure.
EP 0 654 853 B1 reveals a contact spring in the form of a contact spring socket, which has a contact part bent from one piece, with the integrated spring arms thereof being acted upon by additional springs in order to thus ensure the required contact safety. The additional springs are welded to the spring arms and thus are permanently and unreleasably connected thereto. The contact part is a stamped part made from a corresponding sheet metal part and in several bending operations is bent into the final shape, and in the course of this process the additional springs are incorporated which in the assembled state are integrally joined to the spring arms.
Apart from the fact that the design with two parts to be joined during manufacture of the known contact spring results in increased manufacturing expenditure, the influence of welding heat on the spring behavior of the additional spring is disadvantageous.
Furthermore, the constructional design of the known contact spring provides for forwardly opening spring arms formed at the rear end of the contact part. Due to the reduced spring deflection length caused thereby, a reduced spring effect results that can be compensated only by means of the additional spring member.
On the basis of this prior art, it is the object of the invention to indicate a contact spring of the type indicated at the outset, which can be manufactured with as little expenditure as possible and ensures safe functioning. In particular, a multi-piece design is to be avoided while ensuring sufficient contact safety.
According to the invention, this object is met by the characterizing features of claim 1. Additional advantageous developments are indicated in the dependent claims.
Accordingly, it is provided according to the invention that the spring arm bent back into the interior of the contact part is integrally formed on the narrow side of the bottom wall or a side wall on the face side thereof, that at least two additional spring arms are integrally formed laterally at the free end of the bent-back spring arm and are set on edge at an angle, preferably at right angles, and extend with their free ends towards the insertion opening and constitute receptacle for a complementary contact.
Due to the afore-described design according to the invention, in which the two spring arms are provided adjacent the bent-back free end of a contact spring integrally formed on the bottom wall, the invention realizes a quasi doubled spring deflection length with the same short length of the contact part, which has a favorable effect on the resilience behavior of the spring arms and thus on the contact safety of the contact spring.
Furthermore, for improving the contact forces of the contact spring according to the invention, it is advantageously provided that the spring arms are each provided with curved portions facing each other and thus narrowing the cross-section of insertion for a complementary contact in corresponding manner, so that the latter urges the spring arms apart upon insertion thereof. Due to this deflection from the rest position, with the spring arms being expediently biased in the rest position as well, the resetting force of the spring arms, and thus the contact force thereof, is increased.
Backing-up of the spring force, i.e. of the closing or contact force, of the respective spring arm by provision of an additional spring is not necessary with the contact spring according to the invention, but nevertheless may be provided. However, the constructional conception underlying the invention thus is realized in surprisingly simple manner.
In accordance with an expedient development of the invention, the bottom wall is integrally formed with two side walls set on edge in longitudinal direction and one side wall is integrally formed with the top wall set on edge in longitudinal direction, with each of the walls forming right angles with respect to the adjacent walls and the free edges thereof abutting each other, so that said walls, together with the bottom wall, constitute a closed box profile of rectangular cross-section.
In a further improvement of this design, only two opposing spring arms are provided near the insertion opening with the afore-mentioned curved portions each, which are directed towards the longitudinal central axis and which contact each other and thus establish the contact area for a flat complementary contact. The two opposing spring arms in this case are expediently constituted by the angled additional spring arms formed on the bentback spring arm that is integrally formed on the bottom wall.
According to an alternative embodiment, which is provided in particular for pin-shaped complementary contacts, there are provided three walls only, namely a bottom wall and two side walls. The side walls are set on edge along the bottom wall to such an extent that the free edges thereof abut each other and constitute together with the bottom wall a closed box profile of triangular cross-section. The cross-section may also be chosen to be round on the outside and triangular on the inside.
In this respect, it is provided according to a further development that each side wall and the bottom wall have a spring arm associated therewith, with the curved portions thereof contacting each other and establishing a defined contact area for a pin-shaped complementary contact in this case as well.
Irrespective of whether there is a rectangular or a triangular cross-sectional profile of the contact part, the curved portions of the spring arms, according to a further development of the invention, preferably are disposed with the same spacing from the insertion opening each.
For enhancing the contact force of the spring arms, it is provided that each spring arm has a mechanical support disposed on both sides of the curved portion of the respective spring arm each and cooperating with the side wall associated with this spring arm.
Advantageously, the mechanical support of the spring arm integrally formed on the bottom wall is constituted on the one hand by the bending thereof on the bottom wall and on the other hand by abutment on the bottom wall.
The mechanical support of the additional spring arms formed on the bent-back free end of the contact spring formed on the bottom wall is achieved in that these are each supported in front of and behind the curved portion on the associated side wall.
In a further development, the additional spring arms preferably have a centrally formed projection at their free end facing the insertion opening, which engages in a recess formed in the associated side wall and thus establishes a mechanical support for the contact springs. The respective spring arm, by way of the neck-like projection formed thereon, is guided in the recess in the side walls in terms of its height and lateral dimension, while the shoulder-like lateral abutment areas are supported at the edge of the recess, i.e. on the side wall.
Furthermore, the end of the box-shaped contact part directed away from the insertion opening, in a manner known per se, is provided with a terminating device for a connecting cable, which preferably is in the form of a crimp terminal or an IDC terminal.
Another advantageous development of the contact spring according to the invention consists in that the free longitudinal edges of the side walls of the contact part are connected to each other in positive, i.e. form-fitting, manner so that in addition to the bending resistance of the material of the contact part, a resistance in terms of shape has to be overcome as well for damaging the integrity of the contact part. This is achieved in that the free longitudinal edges of the side walls are provided with lugs which are formed on a free longitudinal edge of one side wall of the contact part and engage in slots formed beside the free longitudinal edge of the corresponding side wall of the contact part.
In this respect, it is possible that the lugs formed on a free longitudinal edge of one side wall of the contact part engage through the slots formed beside the free longitudinal edge of the corresponding side wall and optionally are bent over.
These as well as additional advantageous developments and improvements of the invention are subject matter of the dependent claims.